U.S. patent application number 13/009066 was filed with the patent office on 2011-07-21 for heat transfer fluid containing nano-additive.
This patent application is currently assigned to Dynalene Inc.. Invention is credited to Satish Chandra Mohapatra.
Application Number | 20110175017 13/009066 |
Document ID | / |
Family ID | 44276891 |
Filed Date | 2011-07-21 |
United States Patent
Application |
20110175017 |
Kind Code |
A1 |
Mohapatra; Satish Chandra |
July 21, 2011 |
Heat Transfer Fluid Containing Nano-additive
Abstract
A heat transfer fluid comprising a carrier fluid and a
nano-additive is provided. The heat transfer fluid is manufactured
by dispersing the nano-additive in the carrier fluid. The
nano-additive comprises nano-particles having a porous structure
that provides dispersion stability of the nano-additive in the heat
transfer fluid. The nano-additive structure has an aspect ratio of
about 1.0 to about 10,000, a porosity of about 40% to about 85%, a
density of about 0.4 g/cc to about 3.0 g/cc, an average pore
diameter of about 0.1 nanometer to about 100 nanometers, and a
specific surface area of about 1 m.sup.2/g to about 4000 m.sup.2/g.
The nano-additive increases the heat transfer efficiency of the
heat transfer fluid and also reduces the moisture content of the
heat transfer fluid.
Inventors: |
Mohapatra; Satish Chandra;
(Easton, PA) |
Assignee: |
Dynalene Inc.
|
Family ID: |
44276891 |
Appl. No.: |
13/009066 |
Filed: |
January 19, 2011 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61296030 |
Jan 19, 2010 |
|
|
|
Current U.S.
Class: |
252/71 |
Current CPC
Class: |
C09K 5/10 20130101 |
Class at
Publication: |
252/71 |
International
Class: |
C09K 5/00 20060101
C09K005/00 |
Claims
1. A heat transfer fluid comprising: a carrier fluid; a
nano-additive with a porous structure, said nano-additive structure
comprising: an aspect ratio of about 1.0 to about 10,000; a
porosity of about 40% to about 85%; a density of about 0.4 g/cc to
about 3.0 g/cc; an average pore diameter of about 0.1 nanometer to
about 100 nanometers; and a specific surface area of about 1
m.sup.2/g to about 4000 m.sup.2/g; wherein said nano-additive
increases heat transfer efficiency and reduces moisture content of
said heat transfer fluid.
2. The heat transfer fluid of claim 1, wherein said nano-additive
comprises nano-particles having one of a spherical shape, a
cylindrical shape, a plate-like shape, and a fibrous shape.
3. The heat transfer fluid of claim 1, wherein the density of said
nano-additive is about 0.1% to about 10% of the density of said
carrier fluid.
4. The heat transfer fluid of claim 1, wherein the density of said
nano-additive is about 10% to about 200% of the density of said
carrier fluid.
5. The heat transfer fluid of claim 1, wherein said nano-additive
adsorbs from about 1% to about 20% of its weight of moisture from
said carrier fluid in said porous structure of said
nano-additive.
6. The heat transfer fluid of claim 1, wherein said nano-additive
comprises zeolite, silica, alumina, porous carbon, activated porous
carbon, and fibrous carbon.
7. The heat transfer fluid of claim 1, wherein said nano-additive
is about 0.01% to about 20% by weight of said heat transfer
fluid.
8. A method for increasing thermal conductivity and reducing
moisture content of a heat transfer fluid comprising suspending a
nano-additive in said heat transfer fluid.
9. The method of claim 8, wherein said nano-additive has an aspect
ratio of about 1.0 to about 10,000.
10. The method of claim 8, wherein said nano-additive has a
porosity of about 40% to about 85%.
11. The method of claim 8, wherein said nano-additive has a density
of about 0.4 g/cc to about 3.0 g/cc.
12. The method of claim 8, wherein said nano-additive has an
average pore diameter of about 0.1 nanometer to about 100
nanometers.
13. The method of claim 8, wherein said nano-additive has a
specific surface area of about 1 m.sup.2/g to about 4000 m.sup.2/g
and a straight pore geometry.
14. The method of claim 8, wherein the density of said
nano-additive is about 0.1% to about 10% of the density of said
carrier fluid.
15. The method of claim 8, wherein the density of said
nano-additive is about 10% to about 200% of the density of said
carrier fluid.
16. The method of claim 8, wherein said nano-additive adsorbs from
about 1% to about 20% of its weight of moisture from said carrier
fluid in said porous structure of said nano-additive.
17. The method of claim 8, wherein said nano-additive comprises
zeolite, silica, alumina, porous carbon, activated porous carbon,
and fibrous carbon.
18. The method of claim 8, wherein said nano-additive is about
0.01% to about 20% by weight of said heat transfer fluid.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of provisional patent
application No. 61/296,030 titled "Heat Transfer Fluid Containing
Nano-additive", filed on Jan. 19, 2010 in the United States Patent
and Trademark Office.
[0002] The specification of the above referenced patent application
is incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
[0003] This invention, in general, relates to heat transfer fluids
containing a nano-additive, and more particularly, this invention
relates to increasing the heat transfer efficiency and reducing the
moisture content of a non-aqueous heat transfer fluid using a
nano-additive.
BACKGROUND
[0004] Heat transfer fluids are used in a variety of applications
including reactor cooling/heating, plastic molding, constant
temperature baths, automotive coolant systems, cold storage,
climactic chambers, heating, air-conditioning, etc. The primary
objective of a heat transfer fluid is to remove heat from the
source and transfer the heat to a sink. In a typical heat transfer
fluid loop, the heat transfer fluid is pumped through heat
exchangers or jackets. The heat transfer fluid either adds or
removes heat from the process thereby maintaining a stable
temperature.
[0005] Non-aqueous heat transfer fluids are normally used in
extremely low or high temperature applications where water-based
heat transfer fluids cannot operate due to freezing or boiling
problems. Non-aqueous heat transfer fluids have lower heat transfer
efficiency compared to water-based fluids because the non-aqueous
heat transfer fluids have lower specific heat and thermal
conductivity compared to the water-based heat transfer fluids.
Improving the efficiency of a heat transfer process by 20% to 25%
could lead to significant savings in energy and equipment. Hence,
there is a need for improving the efficiency of the heat transfer
fluids.
[0006] Nano-additive particles made from copper, silver, and iron
suspended in a heat transfer fluid improve the thermal conductivity
as well as convective heat transfer coefficient of that fluid.
However, the nano-additive particles do not disperse well in the
heat transfer fluid due to their significant density difference
with the carrier fluid. When surfactants are used to disperse
nano-additive particles in the heat transfer fluid, the surface of
the nano-additive particles gets covered with the surfactant and
diminishes the effectiveness of the nano-additive particles for
enhancing the thermal conductivity of the heat transfer fluid.
[0007] Another common problem associated with non-aqueous heat
transfer fluids is the presence of moisture in the heat transfer
fluid. Moisture could enter into the heat transfer fluid during
installation, or when the heat transfer fluid is re-circulated
during the operation of the system. When a heat transfer fluid goes
through temperature cycles, the expansion and contraction of the
heat transfer fluid allows outside air to contact the heat transfer
fluid. This inflow of outside air into the re-circulating heat
transfer fluid adds moisture to the heat transfer fluid. In low
temperature applications, the moisture can freeze and form ice
crystals in the heat transfer fluid and cause problems in the
re-circulating heat transfer fluid loop. Moisture can also result
in degradation of the heat transfer fluid. In certain applications,
such as in dielectric switches, a very low concentration of
moisture is desired in the heat transfer fluid in order to maintain
a very high dielectric strength of the heat transfer fluid.
Therefore, removal of moisture from heat transfer fluids, or
maintenance of moisture at a certain reduced level is a concern.
Existing methods remove moisture from a non-aqueous heat transfer
fluid by passing the heat transfer fluid through a bed of the
desiccant or molecular sieve. This method could be used in-line or
as a bypass stream of the primary heat transfer fluid loop. If a
desiccant bed is used in-line, the pressure drop in the
re-circulating heat transfer fluid loop increases, thus requiring
the use of a higher horsepower pump. Additionally, the
system/process must be shut down completely in order to change the
desiccant from the re-circulating system. If the desiccant bed is
used in a by-pass stream, that is, a slip-stream, the flow rate of
the heat transfer fluid in this stream is much smaller than the
flow rate in the main heat transfer fluid loop, which in turn
requires an extended time, sometimes months, for removal of the
moisture present in a non-aqueous heat transfer fluid.
[0008] Hence, there is long felt but unresolved need for a heat
transfer fluid that provides better heat transfer efficiency than
its base or carrier fluid and that maintains the moisture content
of the carrier fluid below a threshold level.
SUMMARY OF THE INVENTION
[0009] This summary is provided to introduce a selection of
concepts in a simplified form that are further described in the
detailed description of the invention. This summary is not intended
to identify key or essential inventive concepts of the claimed
subject matter, nor is it intended for determining the scope of the
claimed subject matter.
[0010] The heat transfer fluid (HTF) and the method disclosed
herein addresses the above stated need for improving the heat
transfer efficiency of the HTF as well as removing moisture from a
carrier fluid. The heat transfer fluid disclosed herein comprises a
carrier fluid and a nano-additive suspended in the carrier fluid to
improve the heat transfer efficiency of the heat transfer fluid and
to also reduce moisture in the heat transfer fluid.
[0011] "Nano-additives" as used herein comprise any one or more of
the following: nano-particles, molecular sieves, porous materials,
nano-powders, nano-fibers, and desiccants. These nano-additives are
defined and distinguished based on their properties such as aspect
ratio, size, porosity, etc.
[0012] The nano-additive comprises a highly porous structure
nano-particle, molecular sieve, porous material, nano-powder,
nano-fiber or a desiccant, with a density close to the density of
the carrier fluid to decrease the rate of settling out of the
nano-additive from the carrier fluid in which the nano-additive is
suspended. In an embodiment, the density of the nano-additive is
within about 10% to about 200% of the density of the carrier fluid.
In another embodiment, the density of the nano-additive is within
50% of the density of the carrier fluid. In another embodiment, the
density of the nano-additive is about 0.1% to about 10% of the
density of the carrier fluid, thereby allowing the nano-additive to
be entrained and in a state of suspension in the re-circulating
heat transfer fluid flow. The concentration of the nano-additive is
about 0.01% to about 20% by weight of the heat transfer fluid. The
shape of the nano-additive is, for example, a spherical shape, a
cylindrical shape, a plate-like shape, a fibrous shape or can have
any other shape. The heat transfer fluid is manufactured by
dispersing one or more nano-additives in the carrier fluid. The
nano-additive comprises, for example, zeolite, silica, alumina,
porous carbon, activated porous carbon, and fibrous carbon.
[0013] The nano-additive structure has an aspect ratio of about 1.0
to about 10,000, a porosity of about 40% to about 85%, a density of
about 0.4 g/cc to about 3.0 g/cc, an average pore diameter of about
0.1 nanometer to about 100 nanometers, and a specific surface area
of about 1 m.sup.2/g to about 4000 m.sup.2/g.
[0014] The heat transfer fluid is made by sonication and
homogenization of the nano-additive in the carrier fluid to
disperse the nano-additives in the carrier fluid. The porous
nano-additive improves the heat transfer coefficient of the heat
transfer fluid by increasing the thermal conductivity as well as
the convective heat transfer coefficient of the heat transfer
fluid. The nano-additive also adsorbs and entraps dissolved
moisture inside the porous structure of the nano-additive. In an
embodiment, the nano-additive adsorbs about 1% to about 20% of its
weight of moisture from the carrier fluid in the porous structure
of the nano-additive. The heat transfer fluid and the method
disclosed herein reduce the maintenance costs of the heat transfer
system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 exemplarily illustrates a manufacturing set-up for
manufacturing a heat transfer fluid containing nano-additives.
[0016] FIG. 2 exemplarily illustrates porous nano-additives having
different aspect ratios.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The heat transfer fluid (HTF) disclosed herein is a
non-aqueous fluid containing a nano-additive that increases the
heat transfer efficiency by increasing thermal conductivity of the
heat transfer fluid and reduces the moisture content of the heat
transfer fluid by entrapping water molecules inside its porous
structure. The heat transfer fluid disclosed herein comprises a
carrier fluid and the nano-additive suspended in the carrier fluid.
The nano-additive is, for example, of a spherical shape, a
cylindrical shape, a plate-like shape, a fibrous shape, or a random
shape. In an embodiment, the density of the nano-additive is about
10% to about 200% of the density of the carrier fluid. In another
embodiment, the density of the nano-additive is about 0.1% to about
10% of the density of the carrier fluid, thereby allowing the
nano-additive to be entrained and in a state of suspension in the
re-circulating heat transfer fluid flow. In an embodiment, the
nano-additive adsorbs from about 1% to about 20% of its weight of
moisture from the carrier fluid in the porous structure of the
nano-additive. Also, in an embodiment, the concentration of the
nano-additive is about 0.01% to about 20% by weight of the heat
transfer fluid.
[0018] As used herein, "high thermal conductivity" refers to a
thermal conductivity that is at least 5% higher than the thermal
conductivity of the carrier fluid. Also, as used herein, "low
moisture content" refers to moisture content of less than 200 parts
per million (ppm) in a non-aqueous heat transfer fluid. Also, as
used herein, "carrier fluid" refers to the heat transfer medium in
which the nano-additive is suspended. In an embodiment, the heat
transfer fluid disclosed herein has a thermal conductivity about
10% higher than the carrier fluid. In another embodiment, the
thermal conductivity of the heat transfer fluid disclosed herein is
20% higher than the carrier fluid. In an embodiment, the
nano-particle reduces the moisture content in the heat transfer
fluid to between about 1% to about 100 ppm, for example, 10
ppm.
[0019] The thermal conductivity of the heat transfer fluid
disclosed herein may be measured using any commercially available
thermal conductivity meter. For example, a laser flash based
thermal conductivity meter manufactured by Netschz Instruments
could be used. Separately, hot wire, transient plane or a steady
state method could also be used to determine the thermal
conductivity of the heat transfer fluid.
[0020] The moisture content of the heat transfer fluid may be
measured using any commercially available Karl-Fisher titrimeter. A
coulomatic or a volumetric titrimeter could be used for this
measurement.
[0021] The heat transfer fluid disclosed herein comprises a carrier
fluid, which is a commercially available heat transfer fluid, for
example, a hydrocarbon oil such as Dynalene MV from Dynalene Inc.,
or a silicone oil such as Syltherm XLT from Dow Chemicals, or a
non-aqueous fluid with good thermal and physical properties, for
example, low viscosity and high thermal conductivity and heat
capacity. This carrier fluid should have attributes of a good heat
transfer fluid. These attributes are, for example, low toxicity,
low flammability, high boiling point, and good environmental
characteristics. Examples of carrier fluids are aliphatic and
aromatic hydrocarbons, alkyl aromatics, polyalphaolefins (PAOs),
terpenes, alcohols, ketones, silicones, ionic liquids,
fluorocarbons, perfluorocarbons, chlorofluorocarbons (CFCs),
hydrofluorocarbons (HFCs), perfluoropolyethers (PFEs), and their
mixtures. In the heat transfer fluid disclosed herein, the weight
percentage of the carrier fluid in the heat transfer fluid varies
from about 80 to about 99.9%. The carrier fluid disclosed herein
has a density of about 0.6 g/cc to about 2.0 g/cc. For example, a
linear aliphatic hydrocarbon such as pentane has a density of about
0.6 g/cc, whereas a fluorocarbon could have a density of about 1.8
g/cc.
[0022] The heat transfer fluid disclosed herein comprises a
nano-additive designed to increase the heat transfer efficiency and
reduce the moisture content of the heat transfer fluid. A
nano-additive is defined as a nano-particle, molecular sieve,
porous material, nano-powder, nano-fiber, desiccant or any mixture
of these materials of any shape where at least one of its
dimensions is in the range of 0.5 nanometers (nm) to 5000 nm. The
addition of appropriate nano-additives to a carrier fluid increases
its thermal conductivity significantly. Several mechanisms and
models propose the involvement of Brownian motion of the
nano-additive particles, molecular level layering of the liquid at
the liquid/particle interface, the nature of heat transport in the
nano-additive particles, and the effects of nano-additive particle
clustering in the enhancement of thermal conductivity of the base
fluid. The role of interfacial layers as well as the particle size
in the enhancement of thermal conductivity is well recognized.
Greater thermal conductivity enhancement can be obtained by
lowering the particle/agglomerate size, increasing the particle
thermal conductivity, and increasing the volume ratio of the
particles to the liquid volume. A non-spherical particle or
tubular/rod shapes or linearly aggregated chain-like clusters show
greater thermal conductivity enhancement than a spherical particle.
The fibrous clusters form an interpenetrating network near the wall
of the heat exchanger, thereby improving the heat transfer
properties.
[0023] The effect of fibrous nano-additives on the heat transfer is
profound. Such effect could be three fold: (1) increase of fluid
thermal conductivity, (2) increase of the temperature gradient, and
(3) increase in particle density near the wall due to the Saffman
effect.
[0024] Nano-particles disclosed herein are characterized by
specific values of parameters such as the nano-particle shape,
average pore size, porosity, density, specific surface area, etc.
In an embodiment, the nano-additive is a spherical, micro-porous,
nano-particle. The average diameter of this nano-particle is from
about 0.5 nm to about 5000 nm.
[0025] The average pore size of a nano-particle is the diameter of
the pore in the nano-particle and varies from about 0.1 nm to about
100 nm. The pores could be uniformly or randomly distributed
throughout the interior of the nano-particle. The size distribution
of the pores in a nano-additive could vary significantly. For
example, a nano-additive has pore sizes ranging from about 0.5 nm
to about 10 nm. The smaller size pores are required for the removal
of moisture from the heat transfer fluid, whereas the bigger size
pores are needed to increase the porosity of the particles in order
to bring the nano-additive density closer to the carrier fluid.
[0026] Another parameter of a nano-particle is its porosity.
"Porosity" is defined as the void volume as a percentage of the
total volume of a nano-additive. Porosity is an important parameter
for a nano-additive because porosity determines how much moisture
could be entrapped in the nano-additives as well as the true
density of the nano-additives. A porosity range of the
nano-additives disclosed herein is about 40% to about 85%
range.
[0027] Another parameter of a nano-additive is its aspect ratio.
"Aspect ratio" is defined as the ratio of the length of the
nano-additive to its diameter. For example, a rod-shaped
nano-additive with a length of 5 microns or 5000 nm and a diameter
of 100 nm will have an aspect ratio of 50. Aspect ratio
nano-additives, for example, rods, tubes, plates, etc., improve the
thermal conductivity and the heat transfer efficiency of heat
transfer fluids at a rate higher than the low aspect ratio
nano-additives, for example, spheres. The range of aspect ratio
chosen for the nano-additive disclosed herein is from 1 (sphere) to
10,000 (carbon nano-fibers).
[0028] Another parameter of a nano-additive is its density. The
"density" of the nano-additive is defined as the weight per volume
of each individual particle. Sometimes, it is also referred to as
the "true density" of the nano-additive. For nano-additives
disclosed herein, a density range of 0.4 g/cc to about 3.0 g/cc is
used. A low density nano-additive could be used with a low density
carrier fluid for better stability of the dispersion. Similarly, a
higher density nano-additive could be used with a higher density
carrier fluid.
[0029] Another parameter for the nano-additive is its specific
surface area. The "specific surface area" is defined as the total
surface area, including the pores, in a unit weight of the
nano-additive. The higher the specific surface area, the higher is
the capacity for moisture adsorption. The range for the specific
surface area of the nano-additive disclosed herein is from about 1
m.sup.2/g to about 4000 m.sup.2/g.
[0030] The weight percentage of the nano-additive in the carrier
fluid varies from about 0.01% to about 20% of the weight of the
carrier fluid. The higher the concentration of the nano-additive in
the heat transfer fluid, the higher is the thermal conductivity of
the heat transfer fluid. Higher concentration of nano-additives
also provides moisture removal from the heat transfer fluid for a
longer period of time before the nano-additives are saturated and
need to be replaced.
[0031] Examples of commercially available nano-additive materials
are zeolite, silica, alumina, porous carbon, activated porous
carbon, and fibrous carbon.
[0032] Commercially available zeolite molecular sieve (W. R. Grace
Co., Cambridge, Mass.) are crystalline, highly porous materials,
which belong to the class of alumino silicates. These crystals are
characterized by a three-dimensional pore system, with pores of a
precisely defined diameter. This diameter of the pores is in the
dimension of the size of molecules such as water, CO.sub.2 and
H.sub.2S. The pores can be adjusted to precise uniform openings to
allow for molecules smaller than its pore diameter to be adsorbed
while excluding larger molecules, hence the name "molecular sieve".
The different pore sizes of synthetic zeolites open up a wide range
of possibilities in terms of "sieving" molecules of different size
or shape from liquids.
[0033] Due to the presence of alumina, zeolites exhibit a
negatively charged framework, which is counter-balanced by positive
cations resulting in a strong electrostatic field on the internal
surface. These cations can be exchanged to fine-tune the pore size
or the adsorption characteristics. For instance, the sodium form of
zeolite A has a pore opening of approximately 4 .ANG.ngstrom (0.4
nm), called 4 A molecular sieve. If the sodium ion is exchanged
with the larger potassium ion, the pore opening is reduced to
approximately 3 .ANG.ngstrom (3 A molecular sieve). On ion exchange
with calcium, one calcium ion replaces two sodium ions. Thus, the
pore opening increases to approximately 5 .ANG.ngstrom (5 A
molecular sieve). Ion exchange with other cations is sometimes used
for particular separation purposes.
[0034] The up-take of water in zeolites is called adsorption and
functions on the basis of physisorption. The main driving force for
adsorption is the highly polar surface within the pores. This
unique characteristic distinguishes zeolites from other
commercially available adsorbents, enabling an extremely high
adsorption capacity for water and other polar components even at
very low concentrations.
[0035] Another example of a commercially available nano-additive is
a series of micro-porous carbon nano-particles from Y-Carbon Inc.
(King of Prussia, Pa.). The aspect ratio of these nano-particles is
about 1.0. The porosity of the nano-particles is about 50% to about
80%. The average pore size of the nano-particles varies from about
0.5 nm to about 30 nm. The specific surface area of the
nano-particle varies from about 1500 m.sup.2/g to about 3500
m.sup.2/g. The density of the carbon nano-particles varies from
about 0.17 g/cc to about 1.04 g/cc.
[0036] Another commercial source of nano-additives is a molecular
sieve from Hengye USA, Bensenville, Ill. As an example, their
PG-4AMS molecular sieve has an average pore size of about 0.4 nm.
The density of the particles is about 2.1 to 2.3 g/cc. The
molecular sieve particles are available in diameter range from
about 1.6 mm to about 8 mm. Hence, they have to be milled and
ground to a size range as disclosed herein. Another product from
the same supplier, PG-4AWD, has a particle size (diameter) of 2000
nm to 4000 nm. This material could be used as a nano-additive
directly without any size reduction.
[0037] Another commercial source for several nano-additives is US
Research Nanomaterials, Inc. (Houston, Tex.). The materials
available are aluminum oxide nano-powder (aspect ratio of 1.0,
average particle size of 80 nm and 15 m2/g of specific surface
area), super activated porous carbon nano-powder (particle size:
20-40 nm, pore size 2-5 nm, density: 0.44 g/cc, specific surface
area: 1400 m2/g, aspect ratio: 1.0, and porosity: about 50%),
carbon nano-fibers (density:2.1 g/cc, aspect ratio: 10-250, and
specific surface area: 18 m2/g), super activated carbon nano-powder
(particle size:<100 nm, aspect ratio: 1.0, porosity: 50%,
density: 0.45 g/cc, and specific surface area: 300 m2/g), and
silicon oxide (silica) nano-powder (particle size: 20-30 nm,
density: 2.4 g/cc, specific surface area: 180-600 m2/g, and aspect
ratio: about 1.0).
[0038] Another commercial source for several porous nano-particles
is Nanomaterialstore.com (Fremont, Calif.).
[0039] The nano-additive is added and dispersed in the carrier
fluid, for example, by three methods. In the first method, the
nano-additive is mixed with the carrier fluid in a small mixing
tank, for example, a beaker, at a very high concentration of the
nano-additive, for example, about 20% by weight of the heat
transfer fluid. This concentrated nano-additive dispersion is then
added to the carrier fluid and mixed in a big mixing tank until the
desired concentration of the nano-additive in the heat transfer
fluid is obtained. In the second method, the nano-additive is added
directly to the carrier fluid and mixed with the carrier fluid
until the desired concentration of the nano-additive in the heat
transfer fluid is obtained. In the third method, the nano-additive
or the concentrated dispersion of the nano-additive is added to the
carrier fluid in a heat transfer fluid system. The resultant fluid
is then re-circulated for several hours using the pump in the
system to disperse the nano-additive in the carrier fluid.
[0040] The nano-additive in the heat transfer fluid disclosed
herein may also be removed from the heat transfer fluid when
needed. For example, when the nano-additive gets saturated with
moisture and loses its capacity to absorb moisture from the heat
transfer fluid, the nano-additive may be separated and removed from
the heat transfer fluid and a fresh batch of nano-additive or its
concentrated dispersion may be added directly into the
re-circulating heat transfer fluid loop. The nano-additive
separation could be performed using inline or bypass filters or
cyclone separators.
[0041] In an example of a heat transfer fluid, a dispersion of
alumino silicate (zeolite) nano-additives in a poly alpha olefin
(PAO) fluid is prepared. Normally, alumino silicate is extremely
difficult to stabilize in a hydrocarbon such as PAO due to its
density difference between the heat transfer fluid. Use of a
surfactant or a dispersant to stabilize these nano-additives is
possible, but addition of these ingredients will change the thermal
and physical properties of the PAO fluid, resulting in a less
efficient heat transfer fluid heat transfer fluid HTF. Therefore, a
type of highly porous alumina silicate (molecular sieve) is
purchased and ground to 100 nm size. This provides a nano-additive
with density close to the density of the PAO fluid.
[0042] In another experiment, the nano-additive used was porous
carbon nano-particles from Y-Carbon Inc., King of Prussia, Pa. The
porous carbon nano-particles have a high porosity of about 50% to
about 80% resulting in a nano-particle density within about 10% to
about 50% of the carrier fluids.
[0043] The porous carbon nano-particle adsorbs about 10% of its
weight of moisture at thermodynamic equilibrium. About 0.1% by
weight of this micro-porous carbon nano-particle in the dispersion
adsorbs about 100 ppm of moisture. The micro-porous carbon
nano-particles are dispersed in a carrier fluid using an
ultra-sonication and a homogenization apparatus. Particle size and
moisture content as a function of dispersion time are measured to
determine if the dispersion is stable. A high speed homogenizer was
used to continuously mix the dispersion while the ultrasonic device
broke down the agglomerates.
[0044] A hydrophobic carbon nano-particle was easier to disperse in
a hydrocarbon medium such as the poly alpha olefin (PAO) fluid.
Hydrophilic materials tend to aggregate in a hydrocarbon medium.
Since the densities of these porous carbon nano-particles are
approximately in the same range as that of the carrier fluid, the
porous carbon nano-particles do not settle out from the heat
transfer fluid in the re-circulating heat transfer fluid system,
even if the porous carbon nano-particles aggregate. In an
experiment, dispersions of 200 ml to 500 ml batches were produced
with about 0.1 to 0.5% by weight of porous carbon nano-particles.
Visual checks were performed for any settling of the particles. PAO
samples without porous carbon nano-particles were prepared with
different amount of water content using traditional molecular
sieves and tested. Tests were carried out for particle size using
NICOMP particle size analyzer, stability of dispersion with time
visually, moisture content before and after dispersion, and also
with respect to time by the Karl-Fisher Technique, composition
analysis by gas chromatography and Fourier transform infrared
technique. Thermal conductivities of the carrier fluids with and
without the nano-particle were also determined using a laser flash
apparatus.
Example 1
[0045] A heat transfer fluid composition was prepared using the
following steps:
(1) 500 ml of commercially available hydrocarbon based HTF,
Dynalene MV (Dynalene Inc.), was obtained and placed in a glass
beaker. The glass beaker was placed in an ice bath. A sample of the
fluid was removed and tested for moisture content and thermal
conductivity. (2) 0.42 g of porous carbon nano-particles (from
Y-Carbon, King Of Prussia, Pa.) of an average diameter 20 nm was
added to the hydrocarbon fluid. (3) A homogenizer and a wand type
sonicator were placed in the fluid. (4) Homogenization and
sonication were carried out simultaneously for about 10 minutes.
(5) A sample of the heat transfer fluid was removed and tested for
the nano-additive particle/agglomerate size distribution. An
average size of 120 nm was obtained. (6) A sample of the heat
transfer fluid was also tested for moisture content and thermal
conductivity. (7) The moisture content of the heat transfer fluid
was reduced from about 135 ppm to about 95 ppm and maintained there
for a long period of time. The thermal conductivity of the heat
transfer fluid increased from 0.16 W/m.K to 0.175 W/m.K.
Example 2
[0046] A heat transfer fluid composition was prepared using the
following steps:
(1) 700 ml of commercially available silicone based HTF, Syltherm
XLT (Dow Chemicals, Midland, Mich.), was obtained and placed in a
glass beaker. The glass beaker was placed in an ice bath. A sample
of the fluid was removed and tested for moisture content and
thermal conductivity. (2) 6.0 g of 13.times. molecular sieve
(purchased from Aldrich Chemicals) was ground to 100 nm particles
using a micronizer device. The resultant particles were added to
the silicone fluid in the beaker. (3) A homogenizer and a wand type
sonicator were placed in the fluid. (4) Homogenization and
sonication were carried out simultaneously for about 30 minutes.
(5) A sample of the heat transfer fluid was removed and tested for
the particle/agglomerate size distribution. An average size of 200
nm was obtained. (6) The sample of the heat transfer fluid was also
tested for moisture content and thermal conductivity. (7) The
moisture content of the heat transfer fluid was reduced from about
150 ppm to about 55 ppm and maintained at that level for a long
period of time. The thermal conductivity of the heat transfer fluid
increased from 0.16 W/m.K to 0.19 W/m.K.
Example 3
[0047] A heat transfer fluid composition was prepared using the
following steps:
(1) 500 ml of commercially available hydrocarbon based HTF,
Dynalene HF-LO (Dynalene, Inc., Whitehall, Pa.), was obtained and
placed in a glass beaker. The glass beaker was placed in an ice
bath. A sample of the fluid was removed and tested for moisture
content and thermal conductivity. (2) 20 g of porous and fibrous
carbon material (from Y-Carbon, Inc., King Of Prussia, Pa.) of
average diameter 10 nm and length 1 micron (aspect ratio of 1:100)
was added to the hydrocarbon carrier fluid. (3) A homogenizer and a
sonicator (wand type) were placed in the fluid. (4) Homogenization
and sonication were carried out simultaneously for about 1 hour.
(5) A sample of the heat transfer fluid was removed and tested for
the particle/agglomerate size distribution. An average size of 500
nm was obtained. (6) The sample of the heat transfer fluid was also
tested for moisture content and thermal conductivity. (7) The
moisture content of the heat transfer fluid was reduced from about
200 ppm to about 40 ppm and maintained there for a long period of
time. The thermal conductivity of the heat transfer fluid increased
from 0.16 W/m.K to 0.2 W/m.K.
Example 4
[0048] A heat transfer fluid composition was prepared using the
following steps:
(1) 100 ml of commercially available poly alpha olefin or PAO fluid
(Chevron Chemicals) was obtained and placed in a glass beaker. The
glass beaker was placed in an ice bath. (2) 16.0 g of 13.times.
molecular sieve purchased from Aldrich Chemicals was ground to 100
nm particles using a micronizer device. The resultant particles
were added to the silicone fluid in the beaker to obtain a 20%
concentration by weight. (3) A homogenizer and a sonicator (wand
type) were placed in the fluid. (4) Homogenization and sonication
were carried out simultaneously for about 3 hours, but
intermittently stopping the process to add more ice to the ice
bath. The homogenizer and sonicator produce a significant quantity
of heat when used. (5) The 100 ml concentrated dispersion obtained
in Step 4 was added to a 1000 ml beaker containing 700 ml of PAO
fluid. A mechanical mixer was used to mix the concentrate into the
PAO fluid. (6) A sample of the heat transfer fluid was removed and
tested for the particle/agglomerate size distribution. An average
size of 800 nm was obtained. (7) The sample of the heat transfer
fluid was also tested for moisture content and thermal
conductivity. (8) The moisture content of the fluid was reduced
from about 200 ppm to about 55 ppm and maintained there for a long
period of time. The thermal conductivity went up from 0.15 W/m.K to
0.18 W/m.K.
Example 5
[0049] A heat transfer fluid composition was prepared using the
following steps:
(1) 500 ml of commercially available hydrocarbon based HTF,
Dynalene LO-230 (Dynalene Inc.), was obtained and placed in a glass
beaker. The glass beaker was placed in an ice bath. A sample of the
fluid was removed and tested for moisture content and thermal
conductivity. (2) 10 g of porous silica nano-powder (from US
Research Nanomaterials, Inc., Houston, Tex.) of average diameter
20-30 nm was added to the hydrocarbon fluid. (3) A homogenizer and
a sonicator (wand type) were placed in the fluid. (4)
Homogenization and sonication were carried out simultaneously for
about 1 hour. (5) A sample of the heat transfer fluid was removed
and tested for the particle/agglomerate size distribution. An
average size of 500 nm was obtained. (6) The sample of the heat
transfer fluid was also tested for moisture content and thermal
conductivity. (7) The moisture content of the heat transfer fluid
was reduced from about 200 ppm to about 100 ppm and maintained at
that level for an extended period of time. The thermal conductivity
of the heat transfer fluid increased from 0.16 W/m.K to 0.175
W/m.K.
[0050] FIG. 1 exemplarily illustrates a manufacturing set-up 100
for manufacturing a heat transfer fluid containing nano-additives
103. The nano-additive particles 103 are mixed with a carrier fluid
102 contained in a container 101 to produce the heat transfer
fluid. The porous nano-additive particles 103 are mixed and
dispersed in the carrier fluid 102 using an ultra-sonicator 104 and
a high speed homogenizer 105. The homogenizer 105 is used to
continuously mix the dispersion, while the ultra-sonicator 104
breaks down any agglomerates. Particle size and moisture content as
a function of dispersion time may be measured to determine whether
the dispersion is stable.
[0051] FIG. 2 exemplarily illustrates porous nano-additives 103
having different aspect ratios. High aspect ratio nano-additives
103, for example, rods, tubes, and plates improve the thermal
conductivity and the heat transfer efficiency of the heat transfer
fluid at a rate higher than the low aspect ratio nano-additives
103, for example, spheres. The range of the aspect ratio selected
for the nano-additive 103 is from 1 for spheres to about 10,000 for
carbon nano-fibers.
[0052] The foregoing examples have been provided merely for the
purpose of explanation and are in no way to be construed as
limiting of the present invention disclosed herein. While the
invention has been described with reference to various embodiments,
it is understood that the words, which have been used herein, are
words of description and illustration, rather than words of
limitation. Further, although the invention has been described
herein with reference to particular means, materials and
embodiments, the invention is not intended to be limited to the
particulars disclosed herein; rather, the invention extends to all
functionally equivalent structures, methods and uses, such as are
within the scope of the appended claims. Those skilled in the art,
having the benefit of the teachings of this specification, may
effect numerous modifications thereto and changes may be made
without departing from the scope and spirit of the invention in its
aspects.
* * * * *